In a fuel cell, hydrogen gas or other fuel gas and an oxidant gas containing oxygen are separated by an electrolyte disposed there-between and reacted with each other electrochemically through the electrolyte. Electric energy is extracted directly from electrodes provided on both sides of the electrolyte. Fuel cells are classified based on the type of electrolytic material used. Examples of the main types include phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), and solid polymer fuel cells (PECF).
Solid oxide fuel cells are easy to handle because they use a solid oxide material that is conductive with respect to oxygen ions as the electrolyte. Solid oxide fuel cells have a high electricity generating efficiency and discharge heat at high temperatures. Additionally, solid oxide fuel cells can use a wide range of gases as the fuel gas. For these reasons, solid oxide fuel cells are hopeful candidates for vehicle power source applications and onsite cogeneration system applications.
An example of a conventional solid oxide fuel cell is disclosed in Japanese Laid-open Patent Publication No. 2002-203579. That publication presents a fuel cell made by stacking electricity-generating cells and separators onto each other in an alternating fashion, each electricity-generating cell comprising an air electrode and a fuel electrode arranged on opposite sides of a solid electrolyte layer. The fuel gas is first introduced into a center section from the outside of a separator through a fuel supply passage. The fuel gas then moves along a slit from the center section and is dispensed toward the outside perimeter. The reaction is occurs as the fuel gas moves through the fuel cell.